Typically when that happens, the item will open up with a gray bar at the top and it will say either "This Item Has Been Archived By Enterprise Vault" or "There was an error loading this item"
Once you click the grey banner, it will either give you a pop up with the error message (if it says there was an error) or it will open the message in ViewMessage.asp (if it says the item was archived by Enterprise Vault)
So first thing you should do, is click the grey banner, see what it gives you in terms of error messages
Have the user from their machine go to http://yourEVServer/EnterpriseVault/ and ensure they can search and retrieve messages OK.
Sometimes I have also seen this when the user has recently changed their password and Windows is sending the cached credentials across to the EV Server and you are simply getting an access denied message in the background.
If thats the case you need to clear out the credentials through Managed Passwords in the "User Accounts" section of the windows control panel.
Other things can be that the desktop policy is set to show the contents rather than the original message
or the Outlook vBS DLL file is missing (typically in Terminal Service and Citrix environments)
or that you have Scripting disabled in the inbox, in which case the forms won't function correctly
Other than that though, would really need to see a client trace where the user tries to retrieve the item
https://www.linkedin.com/in/alex-allen-turl-07370146
